Elastic diaphragm switch actuator

ABSTRACT

An elastic diaphragm switch actuator molded from a soft rubberlike material to apply the actuating force to the elastic diaphragm. The actuator has shoulder portions which engage a stop plate to prevent the application of excessive force to the diaphragm member.

mam States Patent Harris et al. 51 Sept. 26, 1972 [54] ELASTIC, DIAPHRAGM SWITCH [56] References Cited ACTUATOR 3 UNITED STATES PATENTS [72] lnvemms: ggig gg g' g g fj 55 swam 3,308,253 3/1967 Krakinowski ..200/159 B 3,517,149 6/1970 Yarborough ..200/172 A [73] Assignee: International Business Machines 2,343,060 2/1944 Homing ..200/159 B Corporation, Armonk, NY. 3,042,764 7/1962 l-lermle ..200/172 X [22] Filed: June 29, 1971 Primary Examiner-H. 0. Jones [211 App! No: 157,909 Attorney-Carl W. Laumann, Jr. et al.

[57] ABSTRACT [52] US. Cl- ..200/ 168 G, 200/172 A, 200/159 B An elastic diaphragm switch actuator molded from a [51] Int. Cl. ..H0lh 9/04, HOlh 3/04 soft rubber-like material to apply the actuating force [58 Field of Search ..200/172 R,1 to h elastic diaphragm The actuator has shoulder portions which engage a stop plate to pre yen t the application of ekcessive force 611w diaph r a grn member.

5 Claims, 6 Drawing Figures PATENTEDSEPZB I972 INVENTORS RICHARD H. HARRIS LOUIS H.8EDARIS BYQQ ATTORNEY ELASTIC DIAPHRAGM SWITCH ACTUATOR BACKGROUND OF THE INVENTION Elastic diaphragm switches have found widespread use in keyboard-type devices. When such switches are used in a keyboard, some mechanism is provided to translate the depression of a key into a force suitable for actuation of the switch.

FIELD OF THE INVENTION This invention relates generally to elastic diaphragm switches'and particularly to actuators suitable for translating the depression of a key-type device into a force suitable for actuation of an elastic diaphragm switch.

DESCRIPTION OF THE PRIOR ART Elastic diaphragm switches such as that shown in the assignees US. Pat. No. 3,308,253 to M. Krakinowski provide a very inexpensive switch for many low current applications. This type of switch is particularly well suited to keyboard applications. In such uses it is desirable to translate the depression of a key into a force which will not exceed the elastic limit of the switch assembly and, at the same time, provide the usual keyboard feel" to an operator.

One such mechanism is shown in the assignees U.S. Pat. No. 3,517,149 to .I. L. Yarborough. That mechanism provides suitable protection for the elastic diaphragm switch. It was effective to substantially extend the life of elastic diaphragm switches. The sole problem with that actuator was the cost of manufacture. In order to obtain the full advantages offered by that actuator, it was necessary to perform individual adjustment on the springs. Once adjusted, the device worked well, but the adjustment process was expensive.

OBJECTS OF THE INVENTION elastic diaphragm switch actuator which does not require adjustment.

Still another object of this invention is to provide an elastic diaphragm switch actuator which applies an accurately controlled force to the diaphragm without the need for adjustment after assembly.

SUMMARY OF THE INVENTION The foregoing objects are achieved by the use of a single spring actuator carrying a molded rubber-like element. The shape of the rubber-like element is such that it provides a dual function. A central columnar portion of the element has a rounded end which depresses the diaphragm. A peripheral shoulder portion comes to rest against a stop plate, thereby allowing the central portion to extend a predetermined distance through the plate to depress the diaphragm.

The element is fabricated as a unitary structure so that the distance which the central element projects above the shoulder can be accurately maintained. Since the element is made as a unitary structure, changes due to shrinkage after molding or variations in material have approximately the same effect on the shoulder portion as they do on the central portion and tend to compensate for each other.

The use of such an element provides an additional benefit in certain configurations by moving the center of percussion of the spring to a point closer to the area of contact. This has the effect of reducing contact bounce.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view, partially in section, of a single key position using the switch actuator of the invention.

FIG. 1A is an enlarged view of the encircled portion of FIG. 1.

FIG. 2 is a view similar to that of FIG. 1 but showing the key in the actuated position.

FIG. 2A is an enlarged and detailed view of the encircled portion of FIG. 2.

FIG. 3 is a partial sectional view of the elastic diaphragm switch actuator.

FIG. 4 is a vector diagram showing the motion of the interposer tip.

DETAILED DESCRIPTION OF THE INVENTION FIGS. 1 and 2 are partial side views of a typical key configuration similar to that used in keyboards.

A key button 10 is affixed to key lever 11. A pivot 12, front guide comb 13, and upstop rod 14 provide for downward movement of key lever 11 about pivot 12 against spring 16 when key 10 is depressed. Key lever 11 carries a dobber 15. When key lever 11 is in the ready position, dobber 15 is lined up with shoulder 20 on interposer 21.

A sliding pivot 22 and rear interposer guide comb 23 support interposer 21 in a fashion which allows the interposer tip 24 to move in the directions indicated by arrows 25a, 25b, and 25c. Spring 26, affixed at one end to interposer 21 and at the other end to rear interposer guide comb 23, urges interposer 21' upward and to the rear. Motion upward is limited by rear guide comb 23 while motion to the rear is limited by sliding pivot 22.

A switch assembly 30 is rigidly supported by frame members not shown in the drawing. The assembly, shown in greater detail in FIG. la, includes elastic diaphragm switches of the type described in US. Pat. No. 3,308,253 to Krakinowski. As shown in FIG. 2a, a substrate 31 having a pattern of conductive lands is spaced from an elastic diaphragm 32, also having a pattern of conductive lands, by separator 33.

Electrical contact between conductive lands on diaphragm 32 and substrate 31 is achieved by distortion of the diaphragm 32. In this embodiment, the distortion is achieved by means of actuator 34 mounted on actuator spring 35. Actuator spring 35 is movable between a cocked position as shown in FIG. 1 and the actuated position as shown in FIG. 2. A stop plate 36, made of rigid plastic or metal, has a plurality of apertures positioned over the movable portions of the diaphragm 32. The apertures are large enough to allow the central columnar portion of actuator 34 to project through stop plate 36 a distance sufficient to move diaphragm 32 and achieve electrical contact between the conductive lands.

The material used to fabricate actuator 34 is rubberlike, for example, Neoprene in accordance with ASTM engagement with diaphragm 32, the central portion is the first to make contact. The application of the full force of spring 35 to the diaphragm 32 is prevented by the limiting action which occurs when the shoulder portion of actuator 34 engages stop plate 36. The actual resulting force exerted by the central portion on diaphragm 32 is determined by the distance which the central portion projects above the shoulder portion. The force can be increased by making this distance greater. It can also be increased by reducing the spring rate of the shoulder portion.

Since both of these variables are determined by the dimensions of the actuator 34, they may be accurately controlled prior to assembly. Thus, no adjustment is required after the device has been put together.

The thickness of stop plate 36 and the characteristics of spring 35 are factors in the system which determines the force applied to diaphragm 32. However, once they are established, these factorsare easily reproduced with great accuracy. In the final analysis, it is the dimensions of actuator, 34 which determine the force applied to diaphragm 32. Since the actuator 34 is molded in a die, the dimensions can be accurately controlled.

There may be very slight variations in different batches of material used to fabricate actuator 34. These variations contribute to dimensional errors due to changes in shrinkage from one batch to the next. In the configuration shown, the variations are largely selfcompensating. If the shoulder portion shrinks, so does the central portion. Assuming that the variation in shrinkage'from one batch to the next is 5 percent, the

actual change in the projection of the columnar portion beyond the shoulder portion would only be 5% of the projection, not 5 percent of the overall dimension.

Subsequent to depression of key and the movement of interposer 21 to release, spring 35, it is necessary to restore the system to enable the next key stroke to be accepted. Restoration is accomplished by restore bail 40 afiixed to armature 41. When restore magnet 42 is de-energized, spring 43 is effective to move interposer 21 forward as shown in FIG. 2. When interposer 21 has moved sufficiently so that shoulder 20 no longer abuts dobber l5, spring 26 causes interposer 21 to move upward into the initial, ready position.

The motion of interposer tip 24 is described by the three vectors 25a-c in FIG. 4. Depression of key 10 results in the downward motion represented by vector 250. When interposer tip 24 reaches the point25a', it

releases spring 35 allowing actuator 34 to close the contacts of the associated elastic diaphragm switch.

A signal generated as a result of the closed switch causes restore magnet 42 to be de-energized. As a result of de-energizing magnet 42, while key 10 is still depressed, spring 43 moves interposer tip 24 along the path described by vector 25b. At point 25b, the shoulder 20 slips off dobber but the inertia of interposer 21 causes it to continue along vector 25b until sliding pivot 22 limits the motion. At this point the action of spring 26 takes over to move the interposer tip 24 along the path described by vector 250. At point 25c, the interposer shoulder 20 engages dobber 15 causing it to tip upward. When' key 10 is released, spring 16 restores the key lever to the original position allowing dobber 15 to return to the position shown in FIG. 1.

The position shown in FIG. 2 corresponds to the intersection of vectors 25a and 25b.

FIG. 3 is illustrative of the general shape of actuator 34. It can be seen that the cross-section of the central columnar portion 50 is less than the area of the shoulder portion 51. Since the actuator is molded from a single material, the shoulder portion 51 will have a higher spring rate that the central portion 50. It can also be seen that the central portion 51 projects beyond the shoulder portion 50. The tip of the central position is rounded in general conformity with the shape taken by the elastic diaphragm 32 in the actuated position shown in FIG. 2a. By conforming to this shape, localized stresses in diaphragm 32 are substantially reduced with a resulting increase in life. 1

A further beneficial effect of the invention, the reduction of contact bounce, is more substantial in some configurations than others. It can be seen that the mass of actuator 34 is effective to move the center of percussion of the spring system closer to the point of contact with elastic diaphragm 32. Moving the center of percussion closer to the point of contact reduces the tendency of the system to oscillate when contact is made.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. In an elastic diaphragm switch assembly having a flexible insulating film carrying bonded conductors engageable with other conductors upon deformation of said film, operating means comprising, I

a. An actuator spring member movable between a cocked position and actuated position,

b. A single piece actuator, molded from a soft rubber-like material, mounted on said spring, said actuator having a peripheral shoulder portion and a projecting central columnar portion, and

c. A stop plate intermediate said spring and said flexible film,

said stop plate having apertures located in positions to allow the projection of said colu nnar portion therethrough to deform said flexible film when said shoulder is in abutting relationship with said stop plate.

2. A device according to claim 1 wherein said shoulder portion hasa relatively higher spring rate than said central portion.

3. A device according to claim 1 wherein the cross sectional area of said shoulder portion is greater than the cross sectional area of said central portion.

4. A device according to claim 3 wherein said actuator has a hardness of approximately Du.

5. A device according to claim 3 wherein the extremity of said columnar portion of spherical in shape. 

1. In an elastic diaphragm switch assembly having a flexible insulating film carrying bonded conductors engageable with other conductors upon deformation of said film, operating means comprising, a. An actuator spring member movable between a cocked position and actuated position, b. A single piece actuator, molded from a soft rubber-like material, mounted on said spring, said actuator having a peripheral shoulder portion and a projecting central columnar portion, and c. A stop plate intermediate said spring and said flexible film, said stop plate having apertures located in positions to allow the projection of said columnar portion therethrough to deform said flexible film when said shoulder is in abutting relationship with said stop plate.
 2. A device according to claim 1 wherein said shoulder portion has a relatively higher spring rate than said central portion.
 3. A device according to claim 1 wherein the cross sectional area of said shoulder portion is greater than the cross sectional area of said central portion.
 4. A device according to claim 3 wherein said actuator has a hardness of approximately 60 Du.
 5. A device according to claim 3 wherein the extremity of said columnar portion of spherical in shape. 